The invention is the first place concerns a power-wrench bolting spindle having a drive shaft and an output shaft which is axially displaceable with respect to the drive shaft against a spring force.
Power-wrenches of this kind are used in power-assembly, for instance in the automobile industry. Illustrative applications are the bolting of an engine block to the supporting vehicle parts, the bolting of the cylinder head cover, and the screwing-together of the components of the connecting rod bearings.
The constant measurement of the depth of bolting is desirable to effectively regulate a bolting procedure. Using a depth sensor, it is possible to decrease the angular speed during the application stage shortly before there is contact between the screw head or nut and the base, whereby the application stage can be terminated with high accuracy when the predetermined applied torque is reached. An accuracy of 1% in the torque is desired.
Depth measurement serves another check: if the screw bore is too shallow or if the thread does not penetrate deeply enough (both being considered a "blind hole"), or if a foreign body is in the bore, then the depth check ascertains simultaneously with the torque verification that while the properly applied torque has been achieved, the required bolting depth has not, and an error signal is emitted.
West German Published Application No. 29 30 430 discloses a bolting spindle of the stated kind. It is equipped with a magnetic sensor (54) detecting the angular position of the drive shaft (26). A bolt is screwed in until its head makes contact with the surface of the associated workpiece. In the course of a second stage, the screw is tightened at a predetermined torque while the angular-position sensor keeps monitoring.
The known bolting spindle does not allow direct depth measurement. Rather, the screw-depth must be computed from the number of revolutions based on the pitch. This entails therefore pre-knowledge of pitch parameters.